Python.NET and VS2010/.NET 4

I hope this will help some people like me searching for an answer. Several steps were mentioned in the Python for .NET mailing list by other people as well, but I haven’t seen a step-by-step guide. It is not my intention to duplicate other posts in that sense, but rather have all-in-one post.

Here is how I’ve got VS2010 and .NET 4.0 working with the revision 122 of the Python.NET having Python 2.6 installed.


  1. Get the sources (tarball from sourceforge or directly from SVN)
  2. Open the pythonnet.sln with VS2010 and convert to 2010 format (will happen automagically)
  3. [updated] Add the constructorbinding.cs to the Python.Runtime.csproj project (see also this post in the PythonNET mailing list)
  4. Change the target framework to 4. Follow the following step for EACH project
    Right-click on the project name and select “Properties”
    Select the “Application” tab on the left (if not selected yet)
    Change the “Target framework” to “.NET Framework 4”
  5. Open the buildclrmodule.bat and change the following lines (2 times!)

    %windir%\Microsoft.NET\Framework\v2.0.50727\ilasm /nologo /quiet /dll %ILASM_EXTRA_ARGS% /include=%INCLUDE_PATH% /output=%OUTPUT_PATH% %INPUT_PATH%


    %windir%\Microsoft.NET\Framework\v4.0.30319\ilasm /nologo /quiet /dll %ILASM_EXTRA_ARGS% /include=%INCLUDE_PATH% /output=%OUTPUT_PATH% %INPUT_PATH%
  6. Open the and change the lines with the version number in the following piece of code.assembly extern mscorlib
    .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )
    .ver 2:0:0:0


    .ver 4:0:0:0
  7. Recompile the whole solution, ignore the deprecation warnings.

Now you have all necessary files under the pythonnet folder where you have the sources. You need clr.pyd, python.exe and Python.Runtime.dll.


  • Run the newly compiled python.exe
    Type the following in the interactive prompt

    >>> import System
    >>> print System.Environment.Version

    The last line proves that you’re using the 4.0 runtime. The precompiled binaries available from SourceForge would show